Workpieces, during the production of which a plurality of work operations, for example forming or cutting, are required, are produced, as a rule, on what are known as multiple-ram transfer presses or press lines. The number of rams corresponds the number of work stages required for production. Transport devices, which transport the workpieces from one machining station to the next, are located between the work stages. In the conventional implementation of these transport devices, gripper or carrying rails, which extend over the entire press length, are moved by means of cam-controlled drives. Gripper or holding elements that hold the workpieces are held during transport, are located on these rails. Characteristics of this type of construction are, on the one hand, the high operating reliability, but, on the other hand, the very large moved masses require correspondingly large drives.
The high costs of these conventional transport devices are one of the reasons for developing electronic transport devices. In this type of construction, the use of cam-controlled drives and of the continuous grip or carrying rails is dispensed with. Instead, each machining stage is assigned individually driven transfer devices. These may be mounted individually and centrally in the run-through direction for each machining stage, but also in pairs and in mirror-symmetry in the column region.
A transfer device of this type is described in detail in DE 100 09 574 A1. In this type of workpiece transport, an intermediate repository that is customary in conventional transport systems is dispensed with. The intermediate repository, also called an orienting station, has the task of varying the orientation of the workpieces between the machining stations so that they could be transported by the following transfer device into the next tool without any variation in orientation.
The transport systems of the more recent generation can carry out this variation in the position of the workpieces between the machining stations during transport. The variation in position may comprise the following axes of movement:
1. horizontal displacement in and opposite to the transport direction;
2. displacement transverse to the transport direction;
3. pivoting in and opposite to the transport direction;
4. pivoting transverse to the transport direction;
5. vertical height variation; and
6. oblique position in the transport direction.
These freely programmable axes of movement or degrees of freedom enable the press operator to stipulate movement characteristics for the transfer that are tool-specific, that is, coordinated with the respective workpiece. The article “Freie Programmierung des Transfers” [“Free programming of Transfer”] from Bleche Rohre profile ½, 98 describes the possibilities and advantages attributed to the use of the freely programmable electronic transfer systems. Due to this high flexibility provided by the free programming of the individual movement axes, there is undoubtedly, as described above, a considerable additional benefit for the press operator. On the other hand, of course, there is also an increase in the requirements for converting the theoretically existing possibilities into a real transfer displacement curve by programming. The high complexity of the overall system makes it difficult for the press operator to optimize the workpiece transport in terms of transport speed or output and freedom from collision.
In order to deal with this problem, a simulator is often employed. This simulator consists of two highly simplified press platens with a transfer unit. The tool bottom parts are located on the platens. In order to make the process of refitting to a new tool set in a transfer press as frictionless as possible, investigations of the transfer movements, in conjunction with the workpiece and the tool bottom parts, are carried out, as early as during the run-in, with the aid of these simulators. This procedure has proved appropriate in the past and is also used frequently.
The disadvantage of this method is that a collision check can take place only between transfer, including the crosshead, tooling and workpiece, and the tool bottom part. Collision with the movable tool top part or the ram or with the following transfer unit cannot be ruled out using the simulator described above. This disadvantage is deliberately taken into account because a simulator set-up including a driven ram and a further press stage would be too complicated and too cost-intensive.
Recently, novel possibilities, which are already partially being utilized, have been afforded by the use of modern 3D-CAD systems with corresponding kinematic modules. The simulator described above is, in this case, replaced by a CAD model, which is a digital map of the press. This CAD model contains at least the interfering edges of the collision-relevant components. By means of appropriate kinematic modules, the moved components are then simulated according to their real movement and are checked in terms of the whole of the movements for collision. Such a simulation method is described in detail in the article “Optimierung von Pressenstrassen durch Simulation” [“Optimization of Press Lines by Simulation”], which appeared in ZWF 9/1997. An attempt is made by simulation to achieve an improvement in output. The main object of optimizing press lines is, in this case, an acceleration of the material flow in the overall system. In movement simulation within the forming press, attempts have been made to take into account physical properties, such as, the oscillation behavior of workpieces or dynamic forces on suction cups, for example. The material flow within a transfer press can be optimized by means of this type of simulation, but, in particular, logistical investigations within a pressing plant can also be carried out.
The disadvantage of this simulation tool is that the operator is not given any aid to more clearly and effectively control the combination of the individual transfer movement axes into an overall movement. As before, the operator must determine the transfer displacement curve by varying the individual drives and by a subsequent synthesis of the movement axes. In modern transfer systems, however, the number of variables is so high that, as a rule, the complexity overtaxes the operator. Consequently, in practice, the displacement curve of electronic transfer is then determined in the same way that was customary in conventional mechanical transfers. The theoretical possibilities provided by electronic transfer systems with freely programmable movement axes are therefore, in practice, not utilized at all or utilized only inadequately by the press operator.